tui: stabilize overview sparklines and prevent wrap artifacts

5 files changed, 47 insertions, 24 deletions

diff --git a/internal/tui/dashboard/layout.go b/internal/tui/dashboard/layout.go
index 38cce18..75cbafb 100644
--- a/internal/tui/dashboard/layout.go
+++ b/internal/tui/dashboard/layout.go
@@ -1,3 +1,6 @@
 package dashboard
 
 const panelHorizontalChrome = 4
+
+// Keep a small guard so sparkline rows never soft-wrap in panel cells.
+const sparklineSafetyMargin = 3
diff --git a/internal/tui/dashboard/overview.go b/internal/tui/dashboard/overview.go
index 9a77da0..990e36d 100644
--- a/internal/tui/dashboard/overview.go
+++ b/internal/tui/dashboard/overview.go
@@ -220,7 +220,7 @@ func summaryBoxInnerWidth(width int) int {
 }
 
 func renderOverviewSparkline(label string, data []float64, panelInner int) string {
-	w := panelInner - utf8.RuneCountInString(label) - 1
+	w := panelInner - utf8.RuneCountInString(label) - 1 - sparklineSafetyMargin
 	if w < 8 {
 		w = 8
 	}
diff --git a/internal/tui/dashboard/overview_test.go b/internal/tui/dashboard/overview_test.go
index 89f00fb..706661e 100644
--- a/internal/tui/dashboard/overview_test.go
+++ b/internal/tui/dashboard/overview_test.go
@@ -117,3 +117,15 @@ func TestRenderOverviewDoesNotOverflowWidth(t *testing.T) {
 		}
 	}
 }
+
+func TestRenderOverviewSparklineHasSafetyMargin(t *testing.T) {
+	const panelInner = 80
+	out := renderOverviewSparkline("Latency:", []float64{1, 2, 3, 4, 5}, panelInner)
+	lines := strings.Split(out, "\n")
+	if len(lines) != 2 {
+		t.Fatalf("expected 2-line sparkline, got %q", out)
+	}
+	if got, max := lipgloss.Width(lines[0]), panelInner-sparklineSafetyMargin; got > max {
+		t.Fatalf("expected sparkline width <= %d with safety margin, got %d", max, got)
+	}
+}
diff --git a/internal/tui/dashboard/sparkline.go b/internal/tui/dashboard/sparkline.go
index 93a6789..2ce8c90 100644
--- a/internal/tui/dashboard/sparkline.go
+++ b/internal/tui/dashboard/sparkline.go
@@ -11,15 +11,23 @@ func renderSparkline(data []float64, width int) string {
 	}
 
 	samples := sampleForWidth(data, width)
+	leftPad := 0
+	if len(samples) < width {
+		leftPad = width - len(samples)
+	}
 	min, max := minMax(samples)
 	if min == max {
 		top := repeatRune(' ', width)
-		bottom := repeatRune('█', width)
+		bottom := repeatRune(' ', leftPad) + repeatRune('█', len(samples))
 		return top + "\n" + bottom
 	}
 
 	top := make([]rune, width)
 	bottom := make([]rune, width)
+	for i := 0; i < leftPad; i++ {
+		top[i] = ' '
+		bottom[i] = ' '
+	}
 	scale := 16.0
 	denom := max - min
 	for i, value := range samples {
@@ -40,7 +48,7 @@ func renderSparkline(data []float64, width int) string {
 			bottomLevel = 8
 		}
 
-		col := i
+		col := leftPad + i
 		top[col] = sparkRowChars[topLevel]
 		bottom[col] = sparkRowChars[bottomLevel]
 	}
@@ -61,24 +69,11 @@ func renderLabeledSparkline(label string, data []float64, width int) string {
 }
 
 func sampleForWidth(data []float64, width int) []float64 {
-	if width == 1 {
-		return []float64{data[len(data)-1]}
-	}
-	if len(data) == 1 {
-		out := make([]float64, width)
-		for i := range out {
-			out[i] = data[0]
-		}
-		return out
-	}
-
-	last := len(data) - 1
-	samples := make([]float64, width)
-	for i := 0; i < width; i++ {
-		idx := int(math.Round(float64(i) * float64(last) / float64(width-1)))
-		samples[i] = data[idx]
+	if width >= len(data) {
+		return append([]float64(nil), data...)
 	}
-	return samples
+	start := len(data) - width
+	return append([]float64(nil), data[start:]...)
 }
 
 func minMax(values []float64) (float64, float64) {
diff --git a/internal/tui/dashboard/sparkline_test.go b/internal/tui/dashboard/sparkline_test.go
index 66d1673..d7acd33 100644
--- a/internal/tui/dashboard/sparkline_test.go
+++ b/internal/tui/dashboard/sparkline_test.go
@@ -16,7 +16,7 @@ func TestRenderSparklineEmptyOrInvalidWidth(t *testing.T) {
 
 func TestRenderSparklineSingleValue(t *testing.T) {
 	got := renderSparkline([]float64{10}, 8)
-	if got != "        \n████████" {
+	if got != "        \n       █" {
 		t.Fatalf("expected two-line constant sparkline, got %q", got)
 	}
 }
@@ -28,14 +28,14 @@ func TestRenderSparklineAllEqualValues(t *testing.T) {
 	}
 }
 
-func TestRenderSparklineStretchesShortHistoryToWidth(t *testing.T) {
+func TestRenderSparklineRightAlignsShortHistory(t *testing.T) {
 	got := renderSparkline([]float64{1, 2, 3}, 6)
 	lines := strings.Split(got, "\n")
 	if len(lines) != 2 {
 		t.Fatalf("expected 2 lines, got %q", got)
 	}
-	if strings.HasPrefix(lines[1], "   ") {
-		t.Fatalf("expected short history to fill width, got %q", lines[1])
+	if !strings.HasPrefix(lines[1], "   ") {
+		t.Fatalf("expected left padding for short history, got %q", lines[1])
 	}
 }
 
@@ -50,6 +50,19 @@ func TestRenderSparklineRespectsWidthTruncation(t *testing.T) {
 	}
 }
 
+func TestSampleForWidthUsesRecentTail(t *testing.T) {
+	got := sampleForWidth([]float64{1, 2, 3, 4, 5, 6}, 3)
+	want := []float64{4, 5, 6}
+	if len(got) != len(want) {
+		t.Fatalf("expected tail length %d, got %d", len(want), len(got))
+	}
+	for i := range want {
+		if got[i] != want[i] {
+			t.Fatalf("expected tail %v, got %v", want, got)
+		}
+	}
+}
+
 func TestRenderSparklineSpansLowToHigh(t *testing.T) {
 	got := renderSparkline([]float64{0, 10}, 2)
 	lines := strings.Split(got, "\n")